Lignin Structural Changes During Liquefaction in Acidified Ethylene Glycol

Abstract

Beech (Fagus Sylvatica) milled-wood lignin was used as a model substrate in a study of lignin-catalyzed liquefaction in the presence of p-toluene sulfonic acid monohydrate (PTSA) or sulphuric acid as the catalysts. The structural changes that lignin undergoes during the treatment were studied by NMR spectroscopy, FTIR, size-exclusion chromatography, and high-performance liquid chromatography. For the sulphuric acid-catalyzed liquefaction, it was shown that the greater hydronium ion concentration in the reaction mixture induced formation of more condensed structures compared to the ones obtained after PTSA-catalyzed liquefaction. In addition, lignin during the PTSA-catalyzed liquefaction suffered degradation and was functionalized by the ethylene glycol. Gradual introduction of the ethylene glycol moieties into the lignin structure formed a condensed lignin-based polymeric material with predominant aromatic hydroxyl groups. HPLC and NMR analysis of the liquefied lignin with low-molecular mass fraction confirmed the presence of lignin monomers and further conversion of initially identified products into the aliphatic, aromatic (syringyl- and guaiacyl-based) esters and acids.     

Fractionation and Characterization of Completely Dissolved Ball Milled Hardwood

Abstract

A simplified method for sequentially dissolving and fractionating ball milled hard wood polymers in high yield is presented. The complete dissolution of the whole ball milled wood, and the fractions recovered from it by applying the sequential fractionation, was accomplished in lithium chloride/dimethylacetamide solvent system enabling size exclusion chromatography studies. The chromatography applied a four detector system; an Ultraviolet-Visible spectroscopy-, Intrinsic Viscosity-Differential Pressure-, Right Angle Laser Light Scattering- and Refractive Index detectors, a combination hereby proposed to enable interpretation of the complex elution profiles with emphasis on chemical interactions. Indirect evidence of the presence of lignin carbohydrate complexes in hardwoods is provided. It is also proposed that cellulose is severely degraded from a degree of polymerization of 10,000 in wood, down to a value of approximately 400 by either the applied ball milling condition or in subsequent solubilization steps.     

Catalytic depolymerisation and conversion of Kraft lignin into liquid products using near-critical water

A high-pressure pilot plant was developed to study the conversion of LignoBoost Kraft lignin into bio-oil and chemicals in near-critical water (350 °C, 25 MPa). The conversion takes place in a continuous fixed-bed catalytic reactor (500 cm³) filled with ZrO₂ pellets. Lignin (mass fraction of approximately 5.5%) is dispersed in an aqueous solution containing K₂CO₃ (from 0.4% to 2.2%) and phenol (approximately 4.1%). The feed flow rate is 1 kg/h (reactor residence time 11 min) and the reaction mixture is recirculated internally at a rate of approximately 10 kg/h. The products consist of an aqueous phase, containing phenolic chemicals, and a bio-oil, showing an increased heat value (32 MJ/kg) with respect to the lignin feed. The 1-ring aromatic compounds produced in the process are mainly anisoles, alkylphenols, guaiacols and catechols: their overall yield increases from 17% to 27% (dry lignin basis) as K₂CO₃ is increased.     

木质素/膨润土吸附处理甲基嘧啶磷废水的研究

以木质素(lignin)改性膨润土(MMT)作为复合吸附剂处理甲基嘧啶磷废水,分别考察了体系pH值、温度、反应时间以及木质素/膨润土的加入量对处理甲基嘧啶磷废水的影响。结果表明,木质素/膨润土处理甲基嘧啶磷废水时,木质素/膨润土加入质量比为5%,pH值为3,温度20℃,吸附时间60 min处理废水效果最佳,嘧啶醇浓度从5 761 mg/L降至130 mg/L,废水COD浓度从12 500 mg/L降至4 033 mg/L。     

A review on lignin-based polymeric,micro- and nano-structured materials

Next to cellulose, lignin is the second most abundant biopolymer, and the main source of aromatic structures on earth. It is a phenolic macromolecule, with a complex structure which considerably varies depending on the plant species and the isolation process. Lignin has long been obtained as a by-product of cellulose in the paper pulp production, but had rather low added-value applications. Changes in the paper market have however stimulated the need to focus on other applications for lignins. In addition, the emergence of biorefinery projects to develop biofuels, bio-based materials and chemicals from carbohydrate polymers should also generate large amounts of lignin with the potential for value addition.These developments have brought about renewed interest in the last decade for lignin and its potential use in polymer materials. This review covers both the topics of the direct use of lignin in polymer applications, and of the chemical modifications of lignin, in a polymer chemistry perspective. The future trend toward micro- and nanostructured lignin-based materials is then addressed.     

Synthesis of soy protein–lignin nanofibers by solution electrospinning

Nanofibers were produced by electrospinning aqueous alkaline solutions containing different mass ratios of soy protein and lignin in the presence of poly(ethylene glycol) coadjutant, all of which presented shear thinning behavior. SEM revealed that the addition of polyethylene oxide as a coadjutant indeed facilitated the formation of defect-free fibers whose diameter increased with lignin concentration, in the range between ≈ 124 and ≈ 400 nm. Favorable interactions between lignin and soy protein were identified from data provided by differential scanning calorimetry. In addition, an increased hydrogen bonding and the loss of secondary structure of the proteins as the lignin concentration increased were observed from the disappearance of amide II (∼1500 cm⁻¹) and III (∼1400–1200 cm⁻¹) bands and a red shift of amide I band in the FT-IR spectrum. The unfolding of the protein contributed to a better interaction with lignin macromolecules, which further improved the electrospinning process. It is concluded that mixtures of lignin and soy proteins, two major renewable resources with interesting chemical features, are suitable for the development of composite sub-micron fibers.     

Coke formation in the co-production of hydrogen and phenols from pyrolysis-reforming of lignin

The phenolics derived from pyrolysis of lignin are important fractions of bio-oil, which could be reformed to generate hydrogen. Nevertheless, some phenolics are value-added chemicals and they might not have to be utilized as source of hydrogen. In this study, we have explored the concept of co-production of hydrogen and phenolics via a pyrolysis-reforming process at the low to medium temperatures of 450–650 °C over Ni/Al₂O₃ catalyst. The results indicated that, below 500 °C, pyrolysis of lignin was almost the exclusive reaction route to form phenolics of varied side chains. The effective reforming of the phenolics initiated at 600 °C and became remarkable at 650 °C. Meanwhile, cracking of the methoxy group and other side chains of the phenolics was also intense at these higher temperatures, producing phenol as the main phenolic compound. Polymerization of the phenolics on Ni/Al₂O₃ catalyst occurred from 450 to 650 °C, while the gasification of the precursors of coke accelerated at 650 °C, forming remarkably lower amount of coke together with enhanced yield of hydrogen. The coke formed from the phenolics was generally the polymeric type with abundant aliphatic structures like C–O–C, –OH and -C-H, low thermal stability, low carbon crystallinity, hydrophilic surface and amorphous morphology at 450–650 °C. The polymerization or cracking of the phenolics could form multiple carbon layers in the vicinity of nickel species, and also on alumina.